Method of working hard brittle metals



June 15, 1965 H L Q 3,189,23&

METHOD OF WORKING HARD BRITTLE METALS Filed Feb. 20. 1961 f?" HMF/AA.

.INV EN TOR.

A 7" TKAQ/VE K United States Patent 3,189,238 METHOD OF WORKING HARDBEETLE METALS John F. Sherrill, Lament Engineering Q0. Inc, Plymouth,Ind. Filed Feb. 20, 1961, Ser. No. 90,4 20 5 Claims. (til. 225-1) Thisinvention relates to a method of working hard brittle metals and is acontinuation-in-part of my copending application, Ser. No. 587,687,filed May 28, 1956, now Patent No. 3,001,279, dated September 26, 1961.

Certain metals which possess valuable physical properties, such as greatstrength, ability to withstand high temperatures, and the like, possessother properties, such as brittleness and frangibility, which make theworking thereof difficult, expensive and time-consuming. Examples ofsuch metals are titanium alloys, magnesium alloys, certain aluminumalloys, and stainless steel, each of which is characterized by extremehardness and brittleness and lack of workability when cold. Thus suchmetals tend to break when subjected to hard or heavy blows, as inpunching and piercing thereof.

As a result of these properties, it has been common heretofore to drillholes to be formed therein, even though the metal is of thin section.

I have found that it is possible to pierce such metals while coldwithout danger of fracture, weakening or otherwise endangering thedesired properties of the metal, and it is the primary object of thisinvention to overcome the disadvantages of hot working methods and toaccomplish effectively, quickly and inexpensively the piercing of hardand brittle metals by a cold working process.

Other objects will be apparent from the following specification.

In the drawing:

The figure is a side view of a piercing method.

My method, broadly stated, entails the piercing of metal by impact athigh speed at a limited area of the work piece while continually andprogressively changing the location of the tool, so that diiferent areasof the Work piece are struck by successive blows, and wherein the blowsare limited to a value less than the physical fatigue limit of themetal.

Referring to the drawing which illustrates the application of my processto the work of piercing sheet metal, the method can be applied to theservice of piercing hard metal sheets by an arrangement as illustratedin FIG. 1, wherein a base or anvil 50 has an aperture or punch hole 52formed therein. The work piece 54 is supported upon the anvil to spanthe punch hole 52, and a punch member 56 concentric with the punch hole52 is reciprocated endwise and is rotated. The punch member 56 has anarrow blade 58 extending diagonally thereof and projecting from the endof the punch, which blade 58 has an end surface substantiallyperpendicular to the axis of the punch. Repeated impacts of the narrowblade 58 at the portion of the sheet 54 which spans the punch opening 52will serve to pierce the sheet and form a hole therein without inpuringthe sheet around the opening.

The hammer member 56 is caused to reciprocate in a directionperpendicular to the work-supporting surface of the member 50 and incoaxial relation with the aperture 52 in the work piece. The rate ofreciprocation will be rapid and preferably substantially uniform. Thusthe reciprocation may be at a slow rate to apply as few as four or fivehundred blows per minute or at higher rates, such as a rate to applysixteen thousand or more blows per minute. The blows will be ofsubstantially uniform value so as to have a predetermined total pressureor impact value per unit of time. In general, the force of theindividual blows will usually be substantially inversely proportional tothe number of blows. Thus each 3,189,238 Patented June 15, 1965 blowdelivered at the rate of 500 blows per minute could be much heavier thanthe individual blows delivered at the rate of 16,000 blows per minute.In all cases care must be taken to limit the force of each blow to avalue less than that which would injure the work piece, i.e., must berestrained within the physical fatigue limits of the material.

Simultaneously with the reciprocation of the hammer 56 to apply blowsrapidly, said hammer is rotated about its axis or otherwise shifted tochange the location of successive blows upon the work area. The hammer56 preferably terminates in a thin longitudinal blade portion 58. As aresult of such formation of the hammer head or blade 58, it will beevident that only a small portion of the area of the sheet which is tobe pierced is contacted by the blade '53 upon each stroke or hammer blowthereof.

As a result of the rapidity of the hammering operation, heat isgenerated within the sheet but the amount of heat usually does notgreatly exceed 100 degrees F. and is not sufficient to cause heat damageto the work piece or expansion thereof. In cases where magnesium alloysare involved, the heat generated will not be suflicient to causecombustion to occur.

As an example of the process, a vanadium type titanium alloy commonlyused for aircraft purposes has a hardness producing a Rockwell A readingin the order of 70. I have found that sheets of this material can beeffectively pierced while cold by using a tool having a blade or.

peen thickness of about ,5 of an inch which is oscillated at the rate ofbetween 6500 and 16,000 blows per minute, and preferably approximately7000 blows per minute, with each blow delivering a force of aboutone-quarter pound in the lower part of the range and reducingprogressively as the frequency of blows is increased, and with thehammer or peen blades being rotated at a speed of approximately 1200revolutions per minute or more. The ratio between the force of the blowsand the frequency of the blows will be such that the total force exertedper unit of time will be substantially the same throughout the fullrange of speed adjustment.

Another example of successful cold piercing of a brittle alloy used inthe aircraft industry and successfully cold pierced by my method isknown as S.T. 6 aluminum alloy. This metal has a Rockwell A rating ofabout 40. In practicing my method on this material, I employ a hammerhaving a blade one-quarter inch thick which is oscillated at the ratefrom 1500 to 3500 blows per minute and preferably approximately 2000blows per minute. Each blow exerts a force of about one pound at thelower end of the range, and less, as one-half pound, at the upper end ofthe range. The hammer is rotated at 1200 rpm. or faster.

In both examples, the width of the blade is substantially less than thetotal area of the surface to be pierced, and the rate of speed ofrotation is such that successive blows by the blade contact differentareas of the work piece within the total area to be pierced. The timerequired for the performance of the piercing operation in both cases isless than the time which would have been required for piercing the samework piece by the conventional drilling methods.

Any means found suitable for controlling the rate of impact, the forceof impact and the rotation of the hammer with respect to the work piecemay be employed. One example of such apparatus is illustrated in myPatent No. 2,876,742, dated March 10, 1959, for Variable Speed FluidPressure Actuation Impact Device, in which a tool is rotatedcontinuously as it is oscillated. Any other apparatus suitable for theperformance of the steps required to rapidly hammer limited portions ofan area to be pierced may be used.

amazes While the preferred steps of the nethod have been described, itwill be understood that the method is not limited precisely thereto, butthat any procedure which falls within the scope of the appended claimsis contemplated within the spirit of the invention.

I claim:

1. The method of forming a circular hole in sheet metal characterized byhardness and brittleness when cold and selected from the groupconsisting of titanium alloys, magnesium alloys, aluminum alloys andstainless steel, consisting of the step of repeatedly and simultaneouslyoscillating and rotating an impact tool having a blade with a fiat endparallel to the metal sheet to be pierced and of a width equal to thedesired diameter of the hole to be formed and a reduced thickness toimpart successively and rapidly to different limited portions only ofthe area of the metal sheet to be pierced, while said sheet is cold andis supported by a member having an opening axially aligned with saidtool and of a diameter slightly greater than the width of said toolblade, blows substantially normal to the metal sheet to be pierced andof substantially uniform force and less than the fatigue limit of themetal, the force of each blow and the width of the impact surface of thetool being inversely proportional to the rapidity of the blow andsufficient to pierce the metal, the direction of said blows beingsubstantially perpendicular to the end of the blade and to the metalsheet to be pierced, and the rotation of said tool producing hammeringof all of the area registering with said opening.

2. The method of forming a circular hole in sheet metal characterized byhardness and brittleness when cold and selected from the groupconsisting of titanium alloys, magnesium alloys, aluminum alloys andstainless steel, consisting of the step of repeatedly and simultaneouslyoscillating substantially perpendicularly to said metal sheet androtating an impact tool having a flat ended blade of a width equal tothe desired diameter of the hole to be formed and a reduced thickness toimpart successively and rapidly to different limited portions only ofthe area of the metal sheet to be pierced, while said sheet is cold andis supported by a member having an opening axially aligned with saidtool and of a diameter slightly greater than the width of said toolblade, blows substantially normal to the sheet metal and ofsubstantially uniform force and less than the fatigue limit of themetal, the force of each blow and the width of the impact surface of thetool being inversely proportional to the rapidity of the blow andsulficient to pierce the metal, and the rotation of said tool producinghammering of all of the area registering with said opening, the rate ofhammering being in a range between 400 blows per minute and 16,000 blowsper minute, the flat end of said blade being substantially parallel tothe metal sheet to be pierced.

3. The method of piercing hard frangible sheet metals having a RockwellA reading in the order of 79 to form a round hole, consisting of thestep of repeatedly and simultaneously oscillating perpendicularly tosaid metal sheet and rotating an impact tool having a flat ended bladeof a width equal to the desired diameter of the hole to be formed and athickness of approximately one-sixteenth inch to impart successively andrapidly to different limited portions only of the area of the metalsheet to be pierced, while said sheet is cold and is supported by amember having an opening axially aligned with said tool and of adiameter slightly greater than the width of said tool blade, blowssubstantially normal to the metal sheet at a rate in the range between6590 and 16,000 per minute and with exertion of a force or".approximately one quarter pound per blow in the lower part of said speedrange and with exertion of inversely proportional force in the upperpart of said speed range, said blows hammering all of the arearegistering with said opening the fiat end of said blade beingsubstantially parallel to said metal sheet.

4. The method of piercing hard frangible sheet metal having a Rockwell Areading in the order of 40 to form a round hole, consisting of the stepof repeatedly and simultaneously oscillating and rotating an impact toolhaving a ended blade of a width equal to the desired diameter of thehole to be formed and a thickness of approximately one-eighth inch toimpart successively and rapidly to different limited portions only ofthe area of the metal sheet to be pierced, while said sheet is cold andsupported by a member having an opening axially alignedwith said tooland of a diameter slightly greater than the width of said tool blade,blows substantially normal to the sheet metal at a rate in the rangebetween 1800 and 3500 per minute each of a force in the range ofapproximately one pound at low speed in said speed range to one-halfpound at high speed in said speed range said fiat tool end beingpositioned parallel to said metal sheet during application of said blowsto said metal sheet.

5. The method of forming a circular hole in sheet metal.

characterized by hardness and brittleness when cold and selected fromthe group consisting of titanium alloys, magnesium alloys, aluminumalloys and stainless steel, consisting of the step of repeatedly andsimultaneously oscillating longitudinally and rotating an impact toolhaving a blade with a flat end substantially parallel to said metalsheet or" a width equal to the desired diameter of the hole to be formedand a reduced thickness to impart succes sively and rapidly to difierentlimited portions only of the area of the metal sheet to be pierced,While said sheet is cold and is supported by a member having an openingaxially aligned with said tool and of a diameter slightly greater thanthe Width of said tool blade, blows substantially normal to the sheetmetal and of substantially uniform force and less than the fatigue limitof the metal, the force of each blow and the width of the impact surfaceof the tool being inversely proportional to the rapidity of the blow andsufiicient to pierce the metal, and the rotation of said tool producinghammering of all of the area registering with said opening, the rapidityand force of the blow and the dimension of the work-engaging portion ofthe tool being substantially in the order and ratio of the followingexamples:

ANDREW R. lUHASZ, Primary Examiner.

CARL W. TOMLIN, HUNTER C. BOURNE,

LEON PEAR, Exm'niners.

1. THE METHOD OF FORMING A CIRCULAR HOLE IN SHEET METAL CHARACTERIZED BYHARDNESS AND BRITTLENESS WHEN COLD AND SELECTED FROM THE GROUPCONSISTING OF TITANIUM ALLOYS, MAGNESIUM ALLOYS, ALUMINUM ALLOYS ANDSTAINLESS STEEL, CONSISTING OF THE STEP OF REPREATEDLY ANDSIMULTANEOUSLY OSCILLATING AND ROTATING AN IMPACT TOOL HAVING A BLADEWITH A FLAT END PARALLEL TO THE METAL SHEET TO BE PIERCED AND OF A WIDTHEQUAL TO THE DESIRED DIAMETER OF THE HOLE TO BE FORMED AND A REDUCEDTHICKNESS TO IMPART SUCCESSIVELY AND RAPIDLY TO DIFFERENT LIMITEDPORTIONS ONLY OF THE AREA OF THE METAL SHEET TO BE PIERCED, WHILE SAIDSHEET IS COLD AND IS SUPPORTED BY A MEMBER HAVING AN OPENING AXIALLYALIGNED WITH SAID TOOL AND OF A DIAMETER SLIGHTLY GREATER THAN THE WIDTHOF SAID TOOL BLADE, BLOWS SUBSTANITALLY NORMAL TO THE METAL SHEET TO BEPIERCED AND OF SUBSTANITALLY UNIFORM FORCE AND LESS THAN THE FATIGUELIMIT OF THE METAL, THE FORCE OF EACH BLOW AND THE WIDTH OF THE IMPACTSURFACE OF THE TOOL BEING INVERSELY PROPORTIONAL TO THE RAPIDITY OF THEBLOW AND SUFFICIENT TO PIERCE THE METAL, THE DIRECTION OF SAID BLOWSBEING SUBSTANTIALLY PERPENDICULAR TO THE END OF THE BLADE AND TO THEMETAL SHEET TO BE PIERCED, AND THE ROTATION OF SAID TOOL PRODUCINGHAMMERING OF ALL OF THE AREA REGISTERING WITH SAID OPENING.